Measurement 732.23 The Tempered Scale ................................................................................................
The equal tempered musical scale is composed of 12 equally spaced intervals separated
by a factor of^122. All notes on the musical scale (excluding sharps and fl ats), however,
are not equally spaced. This is because there are two one-half step intervals on the scale:
that between E and F and that between B and C. The 12 tones, therefore, go as follow: C,
C#, D, D#, E, F, F#, G, G#, A, A#, B, C (see Table 2.10 ).
2.24 Measuring Distortion ...............................................................................................
Figure 2.19 illustrates one of the ways of measuring harmonic distortion. Two main
methods are employed. One uses a band rejection fi lter of narrow bandwidth having a
rejection capability of at least 80 dB in the center of the notch. This deep notch “ rejects ”
the fundamental of the test signal (usually a known-quality sine wave from a test audio
oscillator) and permits reading the noise voltage of everything remaining in the rest of the
bandpass. Unfortunately, this also includes the hum and noise, as well as the harmonic
content of the equipment being tested (see Figure 2.20 ).
Table 2.10 : Tempered Scale
Note Frequency ratio Frequency Hz
C 1.000 262
C#, Db 1.059 277
D 1.122 294
D#, Eb 1.189 311
E 1.260 330
F 1.335 349
F#, Gb 1.414 370
G 1.498 392
G#, Ab 1.587 415
A 1.682 440
A#, Bb 1.782 466
B 1.888 494
C 2.000 523